Process for the manufacture of acrylonitrile synthetic fibers

ABSTRACT

THIS INVENTION CONCERNS A PROCESS FOR THE MANUFACTURE OF ACYLONITRILE SYNTHETIC FIBERS WHERIN AND ACRYLONITRILE POLYMER IS DISSOLVED IN NITRIC ACID FOR PROVIDING A SPINNING LIQUID WHICH IS EXTRUDED INTO A COAGULATION BATH AND COAGUALTED FILAMENTS ARE THEN TAKEN OUT FROM TEH COAGULATION BATH AND WASHED WITH FRESH WATER AND FINALLY DRIED. IN THIS PROCESS SAID SPINNING LIQUID IS PASSED THROUGH A GASEOUS MEDIUM SPACED PROVIDED ABOVE THE FREE LIQUID SURFACE OF SAID BATH UNDER CONDITIONS SUCH THAT EVAPRORATION OF THE SOLVENT NITRIC ACID CONTAINED IN THE EXTRUDED SPINNING LIQUID IS SUPPRESSED AND THE DEGREE OF SWELLIN OF THE PRODUCED FILAMENTS IS MAINTAINED TO LESS THAN 350 WT. PERCENT AND LESS TAHN 300 WT. PERCENT WHEN MEASURED UPON THE COAGULATION AND WATER-WASHING OPERATIONS FOR OBTAINING IMPROVED CHARACTERISTIC OF THE PRODUCED FIBERS.

Jan. 18, 1972 TOSHIO OHFUKA ErAL 3,636,181

PROCESS FOR THE MANUFACTURE OF ACRYLONITRILE SYNTHETIC FIBERS Filed Nov.4, 1968 Patented Jan. 18. 1972 3,636,187 PROCES FOR THE MANUFACTURE OFACRY- LONITRILE SYNTHETIC FIBERS Toshio Ohfuka, Hideo Sato, and KazunoriSagara, Fuji, Shizuoka Prefecture, Japan, assignors to Asahi Kasei KogyoKahushiki Kaisha, Kita-ku, Osaka, Japan Filed Nov. 4, 1968, Ser. No.772,955 Claims priority, application Japan, Nov. 9, 1967, 42/ 71,692Int. Cl. Dlllf 7/00 U.S. Cl. 264-182 Claims ABSTRACT OF THE DISCLOSUREThis invention concerns a process for the manufacture of acrylonitrilesynthetic fibers wherein an acrylonitrile polymer is dissolved in nitricacid for providing a spinning liquid which is extruded into acoagulation bath and coagulated filaments are then taken out from thecoagulation bath and washed with fresh water and finally dried. In thisprocess, said spinning liquid is passed through a gaseous medium spaceprovided above the free liquid surface of said bath under conditionssuch that evaporation of the solvent nitric acid contained in theextruded spinning liquid is suppressed and the degree of swelling of theproduced filaments is maintained to less than 350 wt. percent and lessthan 300 wt. percent when measured upon the coagulation andwater-washing operations for Obtaining improved characteristics of theproduced fibers.

This invention relates to a process for the manufacture of acrylonitrilesynthetic fibers.

It is well known that acrylonitrile synthetic fibers have superiorphysical and chemical characteristics such as favorable feeling andbulkiness, lighter weight, superior warmth retaining performance, andsharp coloring capability.

Formation of dyed specks on synthetic spun fibers is a grave drawbackwhich leads frequently to a considerable reduction in the marketablevalue of the fibers. Especially, in the case of synthetic filamentsincluding those of acrylonitrile, the formation of dyed specks willbecome frequently fatal to the commerciability of the fibrous material.

On the other hand, if fluffy filaments are dyed, the color tone of thedyed product will be dull and pale. If a textile material made fromfluffy filaments is printed, the printed design will be rather blurred.These defects have naturally been long acknowledged as predominantproblems highly difficult to solve by those skilled in the art. Variousproposals have been made in this respect, yet with no effective results.

It is therefore the main object of the invention to provide a highlyimproved process for the manufacture of acrylonitrile synthetic fiberswhich are capable of being dyed with a remarkable evenness and reducingthe formation of disadvantageous flufis thereon to a possible minimum,yet without any appreciable loss of the aforementioned favorablephysical and chemical characteristics.

As is commonly known to those skilled in the art, a process well adaptedfor providing superior synthetic fibers having an improved dyeingperformance for even coloring effect, as Well as a favorable performancecapable of suppressing the formation of naps and flufis to a possibleminimum necessitates a large number of repeated experiments for thedetermination of the well defined and established performance of thedesired effects in the above sense. Upon carrying out these practicaltests, however, we have discovered an improved technique for thefulfilment of the above mentioned object to a satisfying degree.

The invention in its broadest aspect resides in such a process for themanufacture of acrylonitrile synthetic fibers, as comprising steps of:extruding a spinning liquid of an acrylonitrile polymer dissolved innitric acid having a concentration of about 60-80 wt. percent from aspinneret positioned at about 1100 mm. above the liquid surface of acoagulating bath, thus letting the extruded filaments run through thefree air space prevailing between said spinneret and said bath surfaceand under such conditions that the solvent contained in the spinningliquid is subjected to substantially no evaporation; guiding the thusextruded filaments through said bath until the swelling degree of thefilaments amounts to less than 350%; taking the thus coagulated andswollen filaments out of the bath; and washing the filaments by waterfor removing nitric acid therefrom and for keeping the swelling degreeof the thus washed filaments less than 300%.

By adopting the aforementioned improved technique, the generation ofnaps can be reduced to a possible minimum and the coloring performancefor evenness can be highly improved, as will become clear as thedescription proceeds. It has been surprisingly found that in addition tothe aforementioned favorable results, when the thus manufacturedfilaments are subjected to a turbo-stapling step, such as in a perlokmachine, for the manufacture of bulky yarns by providing artificialcrimps at a later stage, conventional trouble caused by the generationof socalled turbo-flies can be substantially obviated in the course ofthe fiber cutting process in the machine.

More specifically, bulky yarns are manufactured preferably in such a waythat two kinds of fibers having different coefiicients of thermalcontraction are mixedly spun and the thus spun yarns are subjected to aheat treatment by contact with a heated medium such as boiling water,stream or the like, thereby causing the more contractive fiber elementsto contract substantially relative to the less contractive elements, forthe generation of a bulkiness of the yarns. This bulky processingtechnique is broadly utilized in the texile industry and for thispurpose, turbo staplers or perlok machines are used in the preparatorystage for cutting the continuously spun filaments into staple fibers. Inthis fiber cutting process, a tow of acrylonitrile filaments is conveyedinto a thermal drafting stage which comprises two hot plates andsubjected to a draft under tension at -160 C. and then cut into fibersby application of impulsive shocks thereto by means of breaker bars.Considerable troubles are encountered frequently, however, by thegeneration of a substantial amount of turbo-flies which consist of wasteshort fibers caused by intense physical and shocking contact of thebreaker bar with the filaments at the very moment of the fiber cuttingoperation. This generation of turbo-flies amounts generally to about0.1% of the tow being treated upon. When the amount of the turboflies islarge, not only the operation of the turbo-stapler may become defective,but also the flies will be driven into and admixed with the sliver, thusresulting in a considerably reduced quality of the yarn spun therefrom.

It is also possible to a certain degree to reduce the generating amountof turbo-flies by adopting properly controlled spinning conditions forthe acrylonitrile filaments being produced with use of nitric acid asthe solvent for the spinning liquid relying upon the wet spinningprocess. But, according to our experiments, the improvement in thisrespect is much to be desired when relying upon the conventionalcomparative technique.

Briefly, the present invention improves the conventional comparativeprocess wherein an acrylonitrile polymer dissolved in a nitric acidsolution to provide a spinning liquid which is then extruded from aspinneret kept immersed in a coagulation bath comprising a dilute nitricacid solution into the latter, and the thus coagulated filaments aretaken out from the bath, washed with water and subjected to severalsteps for drafting, drying and occasional oiling, heating, crimping andothers, mainly in the following three points:

First, the spinning liquid is extruded from a spinneret which ispositioned at 1l00 mm. above the free liquid surface of the coagulationbath thereinto, thereby the extruded spinning liquid runs through thefree air space above the bath surface without substantially any loss ofthe solvent contained in the spinning liquid.

Second, the degree of swelling of the coagulated filaments as taken outfrom the coagulation bath is maintained less than 350%.

Third, the degree of the swelling as washed with water is maintainedless than 300%.

These and further objects, features and advantages of the invention willbecome more clear as the description proceeds by reference to anaccompanying drawing which constitutes part of this specification, aswell as several preferred numerical examples to be set forthhereinafter. It should be however noted that the embodiment shown on thedrawing, and several numerical examples to follow are only illustrativeand in no way limiting.

The drawing shows schematically in section a preferred spinningarrangement adapted for carrying out the process according to theinvention.

In the drawing, numeral 1 denotes a feed pipe which is arranged tosupply from a reservoir and a metering pump, both not being shown, aspinning liquid prepared by dissolving an acrylonitrile polymer innitric acid of about 60-80% concentration, and at a certainpredetermined rate to a spinneret 2 which is of conventional design andformed therein a large number, for instance, 10,000 spinning orifices.The thus extruded spinning liquid is in the form of finely dividedstreams shown schematically at 3 and flows through the free air spacefrom the outlet of said orifices to the free liquid surface of acoagulating bath 4 contained in a reservoir 5 and without any remarkableloss of the solvent contained in the spinning liquid, said bathcomprising a dilute aqueous solution of nitric acid for instance, of33%-concentration. The thus extruded fine streams are introduced intothe bath for coagulation and then taken out by means of rotating rollers6 and 8 mounted as shown. More specifically, these rollers 6 and 8 aredriven to constantly rotate, with the filaments threaded around the bothas at 9. The concentration of the bath and the duration period ofpassage of the thus coagulated filaments through the bath is so selectedthat the degree of swelling of the filaments amounts to less than 350%.The swollen and taken-out filaments are led through a washing bath 7consisting of water and contained in a reservoir 10 for the removal ofnitric acid contained in the coagulated filaments. In this case, theduration period of passage of the filaments through the bath 7 is soselected that the degree of swelling of the filaments amounts to 300% atthe highest. The filaments are then led as at 13 through guide rollers11 and 12 driven by a drive means, not shown, and fed under tensionthrough a drafting bath 14 comprising boiling water and contained in areservoir 15 for subjecting filaments to a draft of 300% or more betweenrotating rollers 11 and 16 and then dried. The filaments at 18 arethreaded around guide rollers 16 and 17 which are driven by a certaindrive means, not shown. The thus drafted and dried filaments may befurther processed by several additional steps for oiling, heat treating,crimping and the like.

In place of the regular homogeneous filaments, the products may becomposite conjugated filaments to be prepared by the conjugated spinningtechnique. The final products may be modified to tows or staple fibers.

Although the true mechanism of the improvements according to theinvention whereby the produced filaments may be dyed surprisinglyhomogeneously, generating a substantially reduced number ofdisadvantageous naps and providing, when treated on the turbo-stapler, aconsiderably reduced amount of turbo-flies, has not yet been ascertainedto a reliable measure, it is believed that for this purpose the specificafiinity of the acrylonitrile polymer to the nitric acid solvent, theinterrelationship between the molecular orientation in the polymersolution as discharged from the spinning orifices of the spinneret and apossible minimum of the evaporation quantity of the solvent contained inthe spinning liquid being kept during the passage of said liquid throughthe free air space from the spinneret to the free surface of thecoagulation bath, and finally the corelationship between thespecifically selected swelling degrees at the respective end of thecoagulation and washing steps with the molecular orientation of thethermally drafted filaments, act in combination and in a highly delicateway for providing a highly stabilized final molecular orientation in thespun and processed filaments.

As was referred to hereinbefore, the spinning liquid used in the presentprocess is a solution of acrylonitrile polymer in nitric acid having aconcentration of 6080% by wt. According to our experiments, it has beenfound that with nitric acid having a concentration lying outside theabove specified range, it is very difiicult to acquire the desirouseffects, even when other spinning and treating conditions are adopted assuggested by the present invention.

When the spinneret is positioned at a closer distance than the abovespecified lowest limit or 1 mm., the bath liquid will arrive at thespinneret outlet along the extruded spinning liquid streams on accountof the inherent surface tension of the bath liquid so that in effect theconventional dip spinning process where the spinneret is completelyimmersed in the bath would be brought about, thus the desirous effectattainable with the present invention would not be realized.

On the other hand, when the spinneret is positioned at a more distantplace than the above specified upper limit or mm., the spun product willrepresent a considerable difference in its coloring performance. In thiscase, the green filaments as extruded from the spinneret are liable toconjoin with each other in the course of passage through the free airspace above the bath surface. In addition, it has been ascertained thatthe thus spun and coagulated final products represent normally a largeamount of naps formed thereon. Therefore, under the above-mentionedspinning condition, it is unable to manufacture superiorpolyacrylonitrile synthetic fibers.

In this respect, sincere care must be taken to carry out the processthat there is practically no evaporation of the solvent contained in thespinning solution in the course of travel thereof through the free airspace and in the form of the extruded fine streams. If not, the desiroushomogeneously coloring performance of the finished fibers will be lostsubstantially. A higher extrusion temperature will invite decidedly thiskind of drawback. Similarly, a higher ambient temperature which affectsupon the prevailing temperature in the free air space in the above sensemust naturally be avoided. The true reason for this drawback is believedto be such that by the evaporation of the solvent to a lesser or largerdegree from the extruded spinning liquid, a delicate and unknownvariation in the dissolved condition of the acrylonitrile polymer in thespinning solution is thereby invited to take place in the directiontowards non-homogeneity.

As already described, the swelling degree of the coagulated filaments atthe outlet of the coagulating bath is adjusted to be less than 350%.When this specified uppermost range is exceeded, the desiroushomogeneity in the coloring performance appearing at a later step may beconsiderably injured. Similarly, alarge amount of naps and turbo-fliesmay frequently be encountered.

The nitric acid component contained in the coagulated filaments must beremoved as much as possible therefrom and for this purpose the filamentsare washed with fresh water. In this case, the degree of swelling of thefilaments is selected to less than 300%, as was mentioned hereinbefore.With a higher degree of swelling, it has been found upon a large numberof our practical experiments that the homogeneously dyeingcharacteristics are substantially affected adversely and the amount ofturbo-flies and naps will be considerably and disadvantageouslyincreased, as with higher swelling degree at the end of the coagulationstep. As an example, the amount of turboflies encountered in the processaccording to this invention will amount generally to 0.20.3 g. per 1 kg.of the filaments, while the value amounts to 0.7l.6 g. if the swellingdegree at this stage is selected to a higher value than above specified.These latter values are considerably inferior to those obtainable withthe conventional compara tive process in which acrylonitrile polymerdissolved in nitric acid is processed according to the normal wetspinning process wherein the amount of the generated turbofiies willamount generally to 0.70.8 g. per kg. of the filaments produced.

Acrylonitrile synthetic fibers as produced by the process according tothis invention indicate those manufactured from acrylonitrile polymersby the wet or dry spinning method or the like. The acrylonitrile polymeras used herein throughout the present invention includes not only thepolymer per se, but also copolymers or a mixture of said polymer andcopolymer. The term copolymer as used throughout the presentspecification should be interpreted as including every copolymer(including block copolymers and graft polymers) of a copolymerizablemonomer with acrylonitrile.

Representative monomers copolymerizable with acrylonitrile andemployable in the present process are acrylic acid; alpha-chloroacrylicacid; alpha-bromoacrylic acid; methacrylic acid, acrylates such asmethylmethacrylate, methoxymethacrylate, ethylmethacrylate,methylacrylate, ethylacrylate, alpha-chloroacrylic acid methyl or -ethylester; vinyl chloride, -fiuoride, or -bromide; vinylidene chloride;methacrylonitrile, acrylamide; methacrylamide; alpha-chloroacrylamideand their alkyl substitutes; methylor ethyl vinylketone; vinylcarboxylates such as vinyl acetate, vinyl chloroacetate, vinylpropionate, vinyl stearate; N-vinyl imids such as N-vinyl phthalimid,N-vinyl succinoimid; methyl malonic acid esters; itaconic acid and itsesters; N-vinyl carbazole; vinyl furan; alkyl vinyl esters; vinylethers; sulfonic acidcontaining monomers such as vinyl sulfonic acid,allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid andits salt compounds: ethylene alpha,beta-dicarboxylic acids, theiranhydrides, esters and amid derivatives; styrene; vinyl pyridine such asZ-methyl- 5-vinyl pyridine; l-vinylimidazole and its alkylatedderivatives such as 2,4- or S-methyl-l-vinylimidazole, and the like.

The spinning liquid is prepared by dissolving the acrylonitrile polymerin nitric acid of about 6080%-concentration. As for the solvent nitricacid, it is preferable to remove therefrom occasionally included nitrouscompounds as carefully as possible. With the use of solvent nitric acideither having a lower concentration than 60% or a higher concentrationthan 80%, it is difficult to obtain the desirous results even when otheroperating conditions should be selected within the respective limits asspecified for carrying out the present invention.

Salts, acid, and like, impurities may be included within a certain rangein the solvent nitric acid without inviting an appreciably adverseeffect if the solvent has a proper acid concentration as abovespecified.

As the process proceeds, the spinning liquid is forcibly extruded fromthe spinneret orifices and the temperature of the liquid should be keptbetween 20 C. and 50 C., preferably between C. and C.

The ambient atmosphere around the spinneret is generally and preferablyselected to be air which constitutes an open atmospheric space. But,under certain circumstances, air may be replaced by an inert gas orgases such as nitrogen, carbon dioxide or the like which shouldpreferably be confined in a limited space. The atmosphere in the abovesense must be preferably kept between -20 C. and 50 C., advantageouslybetween 5 C. and 35 C. It is disadvantageous that the ambient atmosphereshould contain a considerable amount of mist of nitric acid or water,because it will injure the evenly coloring characteristics of themanufactured filaments or the like.

The coagulation bath liquid is composed of nitric acid of l045 wt.percent concentration and the temperature of the bath should be keptbetween 20 C. and 5 C., preferably -10 C. and 0 C. Other acids, saltsand like impurities may be included in the bath without any appreciableadverse effect, if the quantity of the contained impurities is within anallowable range. As shown, the bath may be of the horizontal type. Undercircumstances, however, the bath may be of the vertical type such as thefunnel spinning type. In the latter case, the flow velocity of the bathliquid is so selected that no considerable tension is induced in thegreen filaments as extruded and accompanied by the down-flowing bathliquid. Under these operating conditions, the swelling degree of thespun and coagulated filaments as measured at the outlet of said bathshould be selected to be 350% or less.

The temperature of the Water washing bath providing for the removal ofthe nitric acid content in the spun filaments after coagulation is setto 40 C. at the highest. It is naturally preferable to keep the treatingfilaments under the lowest tension as posible. It is the requisiteoperating condition to keep the swelling degree of the filaments to beless than 300% as measured at the outlet of the water washing bath byproperly selecting the coagulating conditions and the water washingconditions.

The respective swelling degrees of the spun filaments as measured at theoutlets of the coagulating bath and the washing bath vary considerablydepending upon the composition of the polymer, the conditions of thespinning liquid, the coagulating conditions and the like, ranginggenerally from about to about 600%. As a general rule, the swellingdegree of the filaments under treatment will decrease when the polymercontains a hydrophilic copolymer and increases with an increase of thetemperature of the coagulating bath. It will decrease with an increaseof polymer concentration, viscosity of spinning liquid, concentration ofsolvent nitric acid and that of the coagulating acid bath. Underconsideration of these tendencies, the swelling degrees in the abovesense of the filaments under spinning are conditioned to theaforementioned specific ranges.

It has been observed that also in the case of the conventional wetspinning process under utilization of solvent nitric acid as in thepresent case, the swelling degree of the spinning filaments will varyappreciably. But, it should be noted that in such conventionalprocessing modes, the desirous even coloring characteristics, thegenerating degree of disadvantageous naps and the amount of turbofiiesof the filaments in the aforementioned sense do not vary considerablydepending upon the above-mentioned specific operating conditions.

The water-washed filaments are subjected finally to a considerable draftof 300% or more while being heated by contact with boiling water, steamor hot air. In this case, the filaments should be dried preferably undertension to a certain degree. If the filaments not yet dried should beheat treated under slackened conditions, for instance, by contact withboiling water, the generation of naps could be increased considerably,and in addition, the dyeing characteristics would be adversely affectedin the direction of increase of dyed specks when dyed at a later stage.The aforementioned advantageous phenomenon is found to be peculiar tothe process according to this invention, in contrast to the conventionalwet spinning process. Therefore it was found that for carrying out the 7process in accordance with the present invention the filaments should bedried preferably under tension.

The swelling degree as used throughout the present specification ismeasured as follows:

Water and acid are removed from a certain selected amount of thefilaments by centrifuging at 2,000 r.-p.m. with a radius of rotation, 10cm., and for 5 minutes. When the quantity of the polymer contained inthe filaments is expressed by a in grs. and the contained quantity ofwater or water and nitric acid by b in grs., then the swelling degree SDis:

In the following, several preferred numerical examples will be given forbetter understanding of the inventive process.

EXAMPLE 1 A certain quantity of acrylonitrile polymer consisting ofacrylonitrile 90% and methyl acrylate 10% was dissolved in a quantity of70%-nitric acid so as to provide a spinning solution of the polymerhaving a concentration of 18%. On the other hand, a coagulating bath wasprepared by introducing a certain quantity of 30%-nitric acid in a bathvessel such as shown at 5 on the drawing and kept at C. A spinneret washeld at a distance of 3 mm. from the free liquid surface of said bathand the spinning solution at C., was extruded from the orifices of saidspinneret and caused to travel vertically through the free air spaceabove the bath surface into the acid bath. The temperature of theambient atmosphere was 3 C.

The thus coagulated filaments were taken out from the coagulating bathand washed under nearly no tension with fresh water kept at 15 C. Theswelling degrees of the filaments as measured upon said coagulation andwater washing operations were respectively as 241% and 230%. The waterwashed filaments were then drafted in boiling water to 700% of theirlength, and further oiled, dried and crimped as in the usual way.

In this way, a tow of synthetic filaments overall denier being 450,000and monofilament denier being 3, was produced and processed further in aturbo-stapler under the following operating conditions:

Treating temperature measured at hot plate: 140 C. Rate of draft: 139%Depth of breaker bar: 3.11

For comparison purposes, a similar tow was manufactured in accordancewith the comparative conventional process and then equally treated inthe same turbo-stapler. The resulting amount of turbo-flies in bothcases were measured as follows:

Amount of turbo-flies per 1 kg. of resulted fibers Inventive: 0.21 gr.(0.02%) Conventional: 0.80 gr. (0.08%)

EXAMPLE 2 An acrylonitrile polymer comprising acrylonitrile 95%,acrylamide 4.5% and sodium methallyl sulfonate 0.5% was dissolved in75%-nitric acid to provide a spinning solution having a polymerconcentration of 14%. This spinning solution was processed in thefollowing two different ways:

First, the spinning solution, 3 C., was extruded through 100 orifices,each of 0.20 mm. bore, of a spinneret kept at a 5 mm.-distance above acoagulation bath consisting of 33%-nitric acid solution, 3 C., into thelatter. The temperature of the ambient air atmosphere was 3 C. The thuscoagulated filaments were taken out from the bath at a speed of 40m./min., washed with fresh water at 15 C., drafted to 1,000% of theirlength in a steam atmosphere at 100 C., dried under continuous tensionand finally wound up on a conventional winder. The filaments thusproduced represented 2 denier per filament. The

swelling degrees of the filaments amounted respectively to 286% and271%, as measured after the coagulation and water-washing operations.

In contrast to the above-mentioned inventive process, the same spinningsolutions was processed in the comparative conventional process in thefollowing way.

The solution was extruded from 100 orifices, each of 0.09 mm. bore, intoa coagulation bath containing 33%- nitric acid, 3 C. The thus coagulatedfilaments were taken out from the coagulation bath at a speed of 7 m./min., washed with fresh water at 15 C., drafted to 1,000% of theirlength in a steam atmosphere at 100 C., dried under continuous tension,and finally wound up on a conventional winder. The denier per filamentamounted to 2. The degrees of swelling were measured to 316% and 294%,respectively, when measured after the coagulation and water washingoperations.

The number of generated naps and the evenness of the coloringcharacteristics were compared for the both cases. In this case, thelatter data were determined by the following way:

200 grs. of the yarns made of these filaments were knitted on a knittingmachine and the knitted products were refined with a 0.l%-aqueoussolution of Scourol 400, a kind of non-ionic surfactant, comprising asubstantial quantity of polyethylene glycol ether, and then dried. Theseknitted samples were dyed with Astrazon Blue-PG at a dyestufrconcentration: 2% of the overall weight of fibers and with a liquorratio of 1:80 for 1.5 hours.

As for the dyeing evenness, measurements were made of the generatedcolor specks on each of the knitted and dyed samples.

Number of generated naps per 10 meters of fiber bundle Number ofappeared color specks Inventive EXAMPLE 3 Several kinds of spinningsolutions were prepared from an acrylonitrile polymer comprisingacrylonitrile 93% and vinyl acetate 7% and dissolved in nitric acid ofseveral concentrations: 50%, 60%, 70%, and respectively, so as to keepthe polymer concentration at 13%. Each of these spinning solutions wasextruded from orifices, each being of 0.09 mm. bore, of a spinneretwhich was kept at about 1 mm. above the free liquid surface of acoagulation bath consisting of a 35%-nitric acid solution kept at 0 C.,into the bath so as to coagulate. The ambient air atmosphere wasmeasured to 10 C. The thus coagulated filaments were taken out from thebath at a speed of 8 m./min., washed with fresh water at 18 C., draftedto 1,000% of their length in a steam atmosphere at 100 C., dried underconstant tension, and finally wound up by a conventional winder. Theobtained results were as follows:

Degree of swelling,

percent Number of gen- Upon erated Number of Concentration of coagu-Upon naps per color solvent nitric acid lation washing 10 m specks Fromthe foregoing comparative test results, it will be clearly seen thateven if the swelling degrees in the aforementioned sense lie within thespecified range as proposed by the invention, considerable amounts ofgenerated naps and color specks will be encountered, when theconcentration of the solvent nitric acid is selected to be outside thespecified range.

EXAMPLE 4 An acrylonitrile polymer comprising acrylonitrile 95%, methylmethacrylate 4.5% and sodium salt of styrene sulfonic acid 0.5% wasdissolved in 65 %-nitric acid containing about 1% of sodium sulfate forthe preparation of a spinning solution containing 15% of the polymer.Then, this spinning solution was extruded under pressure through 80orifices each being of 0.10 mm. bore, of a conventional spinneret in thefollowing three different ways:

A coagulating bath liquid consisting of a 39%-nitric acid solution wasconstantly recirculated at 2 C. through a bath reservoir, and the aboveprepared spinning liquid, 5 C., was extruded under pressure into thebath liquid after passage through an air space, 5 C., having a traveldistance about 3 mm. for the extruded solution. The thus coagulatedfilaments were taken out under slight tension from the bath at a speedof 7 m./min., washed with fresh water at C., drafted to 1,000% of theirlength in steam at 100 C., dried under constant tension and finallywound up on a conventional winder. The swelling degrees of the thusprepared filaments were measured to 21 and 227%. resnectivelv. at thetermination of the coagulating and water-washing operations.

In a second experiment, the draft was set to about 200% in place of1,000% in the foregoing experiment. Other operating conditions were thesame as above. The corresponding swelling degrees were measured in thiscase to be 203% and 211%, respectively.

In a third experiment, the same coagulation bath as in the foregoingsecond experiment was again employed and the spinning liquid wasextruded from the spinneret at about 50 C., the free air space having apassage distance of about mm., into the coagulation bath. The ambientatmospheric temperature around the spinneret was measured to be 50 C.Other treating conditions were the same as in the first experimentmentioned in the foregoing Example 2. The swelling degrees were measuredrespectively to be 296% and 300% at the end of the coagulation andwater-washing operation.

The evenness of the dyeing characteristics was measured in thelast-mentioned three different experiments, as in the same way in theforegoing Example 2.

Kind of experiment Number of dyed specks First 5 Second 22 Third 51 Thefirst experiment was carried out within the specified conditions asproposed by the present invention. The second experiment was carriedinto effect with a 200%-draft under tension in the coagulation bath. Thethird experiment was performed under such a condition that anappreciable quantity of the solvent nitric acid was dissipated in thecourse of travel of the extruded green filaments through the free airspace. It is clear from these experiments that an application of tensiononto the filaments during passage through the coagulation bath and/or aconsiderable evaporative loss of the solvent nitric acid from the greenfilaments during passage through the free or confined gaseous mediumspace will increase considerably the number of color specks at a latercoloring step of the produced synthetic filaments.

EXAMPLE 5 An acrylonitrile polymer comprising acrylonitrile 90%,methacrylamide 5% and methyl methacrylate 5% was employed as thestarting material for the preparation of the spinning liquid, andsynthetic fibers were prepared therefrom in the following four differentways as shown at I, II, III and IV. The resulted filaments were testedas to the quantity of generated turbo-flies, the evenness of thecoloring characteristics and the amount of generated naps, as in theseveral foregoing experiments. The two last mentioned data weredetermined as in the foregoing Example 2. Turbo-flies were measuredunder the following turbo-stapling conditions:

Remarks: Other operating conditions were same as in the foregoingExample 1.

Turbo-stapling conditions:

H.T., c. 190

H.S., percent 131 Degree of swell Amount Upon of tu'rbo- Number NumberKind of coagu- Upon flies per of naps of color spinning lation washing 1kg. per 10 m specks From the foregoing, it will be clear that in theboth cases I and II where the swelling degrees were set far from thespecified range as proposed by the present invention, the results werehighly inferior. In the third case III where only the swelling degree offilaments as measured upon the water-washing operation is far from therecommended range, results were also considerably inferior.

EXAMPLE 6 An acrylonitrile polymer comprising acrylonitrile methylacrylate 8% and allylsulfonic acid 2% was dissolved in 65%-nitric acidso as to provide a spinning solu tion having a polymer concentration of14%, while a 35 %-nitric acid solution, kept at 2 C., was recirculatedthrough a horizontal type coagulation bath tank. Then, the spinningsolution, 0 C., was extruded through orifices, each being of 0.20 mm.bore, through variously different air passages of 5, 25, 50, 100 andmm., into said acid bath. The ambient temperature around the spinneretwas measured to 15 C. Measures were adopted to keep the ambientatmospheric air around the spinneret in a stationary condition. The thuscoagulated filaments were deflected to change their travel passagedirection and then taken out by means of a rotating roller from thecoagulation bath at a speed of 10 m./min. Then, they were washed withfresh water at 15 C. and drafted 1,000 of their length in steam at 100C. The swelling degree of the filaments was measured, respectively, tobe 281% and 267% after the coagulation and water-washing operations.Then, the filaments were dried continuously under tension and finallywound up upon a conventional winder. In this way, five different groupsof 100 filaments, each 2 denier, were obtained and the results werecomparatively determined as in the case of the foregoing Example 2.

Number Throughout this specification, it must be noted that all theparts and percentages, except degree of swelling, have been given byweight.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the inventionprinciples, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What we claim is:

1. A process for the manufacture of acrylonitrile synthetic fiberscomprising preparing a spinning solution by dissolving a polymerselected from the group consisting of a homopolymer of acrylonitrile andcopolymers of acrylonitrile and monomers copolymerizable therewith innitric acid having a concentration of from 60 to 80 weight percent, andwherein the temperature of said spinning solution varies from 20 C. to50 C., extruding all of said spinning solution through a spinneret whichis disposed from 1 to 100 mm. above the surface of a coagulating baththrough a gaseous medium into said coagulating bath, wherein saidcoagulating bath comprises an aqueous solution of nitric acid having aconcentration of from to 40 weight percent wherein the temperature ofsaid gaseous medium varies from 20 to 50 0, wherein the temperature ofsaid coagulating bath varies between 20 and 5 C., whereby theevaporation of nitric acid solvent of said spinning solution is substantially depressed, guiding the resulting filaments through saidcoagulating bath wherein the swelling of said filaments exiting fromsaid coagulating bath is less than 350 weight percent, washing theresulting filaments have a swelling of less than 300 weight percent,stretching the filaments to at least 300% and drying the filaments.

2. A process as set forth in claim 1 wherein said gaseous medium isatmospheric air, carbon dioxide or nitrogen.

3. A process as set forth in claim 1 wherein the drying of saidfilaments is carried out under tension.

4. The process as in claim 1 wherein the temperature of said spinningsolution varies from 10 to 20 C., wherein the temperature of saidgaseous medium varies between -5 and (3., wherein said gaseous medium isselected from the group consisting of atmospheric air, carbon dioxideand nitrogen, and wherein the temperature of said coagulating bathvaries between 10 and 0 C.

5. The process as in claim 1 wherein said polymer is a homopolymer ofacrylonitrile or a copolymer of acrylonitrile with a monomer selectedfrom the group consisting of methylacrylate, acrylamide, sodiummethallyl sulfonate, vinyl acetate, methyl methacrylate, sodium salt ofstyrene sulfonic acid, methacrylamide, and allyl sulfonic acid.

References (Zited UNITED STATES PATENTS 2,957,748 10/1960 Lieseberg264206 3,073,669 l/1963 Fujisaki et a1 264206 3,088,793 5/1963 Knudsenet a1 264-210 3,107,971 10/1963 Yasawa et al. 26438 3,147,322 9/1964Fujisaki et al. 264182 3,410,941 11/1968 Dagon et al 264-182 3,412,19111/1968 Kitajima et a1. 264182 2,367,493 1/1945 Fordyce et a1. 264203JAY H. WOO, Primary Examiner US. Cl. X.R. 264-203

